It happened on Thursday in the 4600 block of San Francisco Ave, in the Penrose neighborhood of North St. Louis. The 20-year-old, who police say has a mental disability, was playing with a shotgun and accidentally shot 15-year-old Alicia Anderson.

Police say the mother told them the gun belonged to a family friend who left it there.

"She apparently thought she had hid the gun well-enough that nobody would find it until she was able to properly dispose of the weapon," St. John Green said.

Anderson's boyfriend was in the house when it happened, and he ran down the street to get help. Sources say the gun was spray-painted gold, which could possibly be a reason why Marcus Anderson didn't think it was real.